LNT and DPF Regeneration via Periodic Rich-Lean Cycling
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Solution Overview
Problem
Current methods for purifying exhaust gases from internal combustion engines, particularly diesel engines, face challenges in efficiently regenerating Lean NOx traps (LNTs) and particulate matter filters without increasing fuel consumption, while avoiding sulfur poisoning and high-temperature damage to these components.
Innovation Solution
A method and system that alternates between rich and lean exhaust gas mixtures to simultaneously de-sulfurize the LNT and regenerate the particulate matter filter, using a control unit to manage the engine's operation and maintain optimal temperatures and oxygen levels, thereby minimizing fuel penalty and preventing H2S emissions and thermal damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the engine is operated with a rich exhaust gas mixture for a prolonged period to de-sulfurise the LNT, then the sulfur compounds are effectively removed from the LNT, but H2S emissions increase and fuel consumption rises
Solution Approach 1:
The patent applies periodic action by alternating between rich and lean exhaust gas phases in a controlled cycle. The rich phase duration is limited to a specific time window (e.g., 5-15 seconds) followed by a lean phase, creating a periodic regeneration pattern that prevents H2S accumulation while maintaining LNT performance. This periodic switching allows sulfur removal without prolonged rich operation that would generate excessive H2S.
Solution Approach 2:
The patent utilizes parameter changes by dynamically adjusting the air/fuel ratio (lambda) between rich (lambda < 1) and lean (lambda > 1) states, and by controlling exhaust gas temperature within specific ranges (e.g., 250-450°C during rich phase, higher during lean phase). These parameter transitions enable effective de-sulfurisation while preventing H2S emissions through controlled chemical conditions.
2Reliability
If the engine is operated with high exhaust gas temperature to regenerate the particulate matter filter, then soot is effectively oxidized, but thermal damage to the filter and increased fuel consumption occur
Solution Approach 1:
The patent employs periodic action by implementing cyclic transitions between rich and lean phases, where the lean phase provides the necessary temperature elevation for soot oxidation but is limited in duration. This periodic approach allows the filter to reach regeneration temperatures without sustained high-temperature exposure that would cause thermal damage. The cycle repeats only when regeneration is complete, preventing overheating.
Solution Approach 2:
The patent applies continuity of useful action by ensuring that the rich phase continuously reduces sulfur compounds and prepares the exhaust gas composition, while the subsequent lean phase continuously provides oxygen for soot oxidation. This continuous alternating action maintains optimal conditions for both LNT de-sulfurisation and DPF regeneration without interruption or excessive temperature spikes.
3Reliability
If separate regeneration processes are used for LNT de-sulfurisation and DPF regeneration, then each component can be optimized independently, but the overall process time and fuel consumption increase
Solution Approach 1:
The patent merges the LNT de-sulfurisation process and DPF regeneration process into a single integrated exhaust gas treatment cycle. By combining these two functions into one periodic rich-lean alternating sequence, the system achieves both sulfur removal and soot oxidation simultaneously, reducing the total time required compared to performing separate regeneration operations. The rich phase addresses LNT sulfur while the lean phase addresses DPF soot, both within the same operational cycle.
Solution Approach 2:
The patent applies universality by designing the exhaust gas treatment system to perform multiple functions through a single control strategy. The periodic rich-lean cycle serves dual purposes: de-sulfurising the LNT during the rich phase and regenerating the DPF during the lean phase. This multi-functional approach eliminates the need for separate dedicated regeneration procedures, reducing overall process time and fuel consumption while maintaining component-specific optimization.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach maintains NOx conversion efficiency, reduces fuel consumption, and minimizes the risk of sulfur poisoning and thermal damage, allowing for periodic and efficient regeneration of both components with reduced emissions and improved engine performance.
Implementation Method 1
In an LNT, the NOx compounds in the exhaust gas will be adsorbed by means of a NOx storing compound such as barium
Implementation Method 2
Such a filter is suitably also provided with an oxidizing catalyst for oxidizing, i.e. removing, hydrocarbon compounds (HC) and carbon monoxide (CO) in the exhaust gas
Implementation Method 3
Such a raised temperature is normally provided by means of so-called post-injections of fuel, i.e. injections of fuel during a late stage of the combustion procedure. Such post-injections generate a relatively high amount of heat
Implementation Method 4
the LNT must be regenerated, which means that it must be brought to desorb, i.e. release, the accumulated NOx compounds
Data Source
AI summary
The invention relates to a method for purifying exhaust gas in an internal combustion engine provided with an LNT and a particulate matter filter arranged in an exhaust gas conduit of the engine. The method includes de-sulfurization of the LNT and regeneration of the particulate matter filter. The invention includes the following steps: initiating a heating phase wherein the engine is set to generate heat sufficient for the de-sulfurization and the regeneration; initiating a de-sulfurization phase during a first time period (t1), in which the engine is set to generate a rich exhaust gas in the exhaust gas conduit; keeping the first time period below a first maximum value so as to avoid release of emissions of H2S from the engine; initiating a regeneration phase during a second time period, in which the engine is set to generate a lean exhaust gas in the exhaust gas conduit; keeping the second time period below a second maximum value so as to avoid thermal damage to the particulate matter filter; and repeating the de-sulfurization phase and the regeneration phase in a periodical manner.